The Upper Pennsylvanian rocks in eastern Shawnee County and vicinity were deposited during alternating marine and nonmarine conditions. Sedimentation in the Late Pennsylvanian sea was cyclic; the depositional sequence of marine beds in both the Shawnee and Wabaunsee Groups was in a definite order, although the order is different in the two groups.

The Late Pennsylvanian sea advanced from the southwest (Wanless, 1950, p. 20). The depth of water was estimated by E. L. Yochelson (written commun., 1960) to have been not more than 50-75 feet, and by Moore (Wanless, 1950, p. 26) to have been less than 100 feet. Elias (1937, p. 421) estimated that the maximum depth of the late Paleozoic sea in Kansas was about 180 feet. The sediment supplied to the sea was derived mainly from an upland to the east and south (Moore, 1929, p. 483).

The lower part of the Snyderville Shale Member of the Oread Limestone, the oldest exposed bedrock in the area, may have been deposited in a nonmarine environment, but the upper few feet of the Snyderville was laid down in a shallow sea, as indicated by a marine fauna. The depth of the sea probably increased gradually, for the abundance of fusulinids in the middle part of the Leavenworth suggests deposition in quiet water, in an environment similar to that postulated by E. L. Yochelson (written commun., 1960) for the Big Springs Limestone Member of the Lecompton Limestone. Partly on the basis of the abraded appearance of the fossils, however, Dixon (1960, p. 36) suggested that the middle part of the Leavenworth was deposited in more turbulent and probably shallower water than other parts of the limestone.

The lower part of the overlying Heebner Shale Member accumulated as black mud, probably in very shallow water, under reducing conditions favorable for the growth of conodonts and the formation of phosphatic nodules. These conditions were similar to those that prevailed during deposition of the Chattanooga Shale (Late Devonian in central Tennessee (Conant and Swanson, 1961, p. 56, 62). The gray marine shale in the upper part of the Heebner indicates that a well-aerated and presumably, gradually deepening sea persisted during deposition of the Plattsmouth Limestone Member of the Oread Limestone. The abundant fauna (dominantly brachiopods), wavy bedding (possibly due to currents), and many thin claystone partings seem to indicate that deposition occurred in a relatively shallow-water environment in which the depth of water, position of the strand line, and, probably, the source of sediment varied repeatedly. The overlying Heumader Shale Member presumably was deposited mainly near shore in a retreating sea. The sparse marine fauna locally present in the uppermost part of the shale outside eastern Shawnee County and vicinity indicates a minor readvance, or at least a temporary halt, in the general regressive phase of the sea during which the Kereford Limestone Member of the Oread was deposited. Monger (1961, p. 49) concluded that the lower part of the Kereford was deposited during quiescent marine conditions and that the upper part was deposited above wave base, which resulted in the sorting of fossil fragments and the winnowing of calcareous ooze.

After deposition of the Oread Limestone, the accumulation of a thick section of nonmarine clastics formed the Kanwaka Shale. The readvance of the sea, during which the thin fossiliferous Clay Creek Limestone Member was deposited, temporarily interrupted these nonmarine conditions. The Late Pennsylvanian sea returned to this general area before deposition of the Lecompton Limestone, as indicated by the occurrence of a sparse molluscan fauna in the upper part of the Kanwaka.

Strata were deposited in the same cyclic sequence, probably under very similar environmental conditions, during Lecompton time as were the beds of the Oread Limestone. The initial unit of the Lecompton Limestone--the lower part of the Spring Branch Limestone Member--contains abundant fusulinids and a few other fossils and probably was deposited in quiet water that was perhaps deeper than normal marine but was certainly shallow enough for food to be abundant (E. L. Yochelson, written commun., 1960). The presence of algae, gastropods, and some ostracodes in the upper part of the Spring Branch indicates that the water became shallower. Carbonaceous material in the overlying Doniphan Shale Member suggests nonmarine or perhaps estuarine conditions, which were followed by a deepening of the sea and the deposition of the fusulinid-bearing Big Springs Limestone Member. The presence of algae in the upper part of the Big Springs may indicate a shallower water environment in late Big Springs time. The Queen Hill Shale Member, which consists of black claystone overlain by gray claystone, accumulated under conditions similar to those that existed during Heebner time. Abundant fusulinids, echinoderm debris, large pieces of bryozoans, and abundant and varied brachiopods in the Beil Limestone Member of the Lecompton indicate normal-marine fairly quiet water (E. L. Yochelson, written commun., 1960). The local occurrence of algae and the alternating beds of limestone and claystone, particularly in the upper part of the Beil, bear record of variations in the depth of water and in the types of available sediment. The sea was withdrawing from this part of the State in early King Hill time, and the area may have been emergent for at least part of that time. Ostracodes and foraminifers in the upper part of the King Hill Shale Member show that there was a return of shallow marine waters. The water became deeper during accumulation of the lower fusulinid-bearing part of the Avoca Limestone Member but again became more shallow as the upper part was deposited.

As the sea continued to retreat, the foraminifer- and ostracode-bearing basal few feet of the Tecumseh Shale was deposited. During most of the Tecumseh time, subaerial conditions existed, as indicated by the presence of a thick section of clastics containing plant remains but no marine fossils. A transgressing sea moved into this area in late Tecumseh time, as recorded by the marine fauna in the upper part of the formation.

During Deer Creek time the transgressive and regressive movements of the sea, the environments of deposition, and the resulting strata were virtually identical to those during Oread and Lecompton time and occurred in about the same order. After deposition of the lower, fusulinid-bearing part of the Ozawkie Limestone Member of the Deer Creek Limestone, conditions rapidly changed to a beach or extremely shallow-water environment in which the dominantly algal limestone in the upper part of the Ozawkie was formed (E. L. Yochelson, written commun., 1960). The sea retreated briefly in early Oskaloosa time, but returned in late Oskaloosa time and remained all of Rock Bluff time. The reducing marine environment that existed earlier in Heebner and Queen Hill times recurred in early Larsh and Burroak time, Deepening of the Late Pennsylvanian sea reestablished normal marine conditions, under which the upper part of the Larsh and Burroak Shale Members and the Ervine Creek Limestone Member accumulated.

Gradual withdrawal of the sea at the end of Ervine Creek time resulted in estuarine or very shallow water near-shore marine conditions in earliest Calhoun time, as indicated by the presence of Lingula and algal-coated myalinid pelecypods in the basal part of the Calhoun Shale (E. L. Yochelson, written commun., 1960), Eastern Shawnee County and vicinity was largely emergent during deposition of the noncarbonate clastics of the Calhoun; plant remains, interformational channeling, and rapid lateral variations in types of sediment suggest that flood-plain conditions existed. In late Calhoun time swamp conditions locally prevailed for a short time, as shown by the presence of a thin coal bed near the top of the formation. Thin fossiliferous limestone beds locally present in the upper part of the Calhoun indicate that some parts of the area were not emergent during Calhoun time.

Strata of the Topeka Limestone are dominantly marine. The lower two limestone members of the Topeka--the Hartford and the Curzon--probably were deposited under generally similar conditions in an environment that varied from normal marine with fairly quiet water to one in which the water was shallower and the circulation more vigorous (E. L. Yochelson, written commun., 1960); the more vigorous circulation is suggested by the presence of bioclastic limestone in part of the Curzon. The presence of algae in both the Hartford and the Curzon indicates that the water was shallow enough for photosynthesis to take place (E. L. Yochelson, written commun., 1962). The intervening Iowa Point Shale Member probably is largely marine, but the presence of abundant carbonized plant fragments suggests that estuarine conditions may have existed locally. The few brachiopods and pelecypods locally present in the Jones Point Shale Member suggest marine deposition, but there is no evidence to indicate the depositional environment of the unfossiliferous parts. The presence of abundant algae suggests that during Sheldon time the sea must have been relatively shallow, and probably clear. A fresh-water pool or swamp environment in which ostracodes and plants were dominant may have existed at least locally in the area when the basal part of the Turner Creek Shale Member of the Topeka Limestone was laid down. A change to a marine environment is indicated by the presence of brachiopods and pelecypods in the rest of the Turner Creek, and the sea remained in the area during deposition of the Du Bois Limestone Member. The black claystones in the lower part of the Holt Shale Member probably were deposited in very shallow poorly oxygenated waters. The sea progressively readvanced over the area in late Holt time, and marine conditions prevailed during deposition of the very fossiliferous limestones of the Coal Creek Limestone Member of the Topeka.

This part of Kansas was emergent at the end of Topeka time, and the nonmarine Severy Shale was deposited. The initial Severy deposits as well as beds of the underlying Topeka Limestone were removed from part of the area by stream channeling. Recurrent erosion is also recorded by the presence of channel deposits stratigraphically higher in the Severy.

A sparse marine fauna in the upper part of the Severy records a marine invasion of short duration, but the marine conditions soon were replaced by widespread swamp conditions favorable to the accumulation of carbonaceous materials, notably the Nodaway coal bed at the base of the Howard Limestone. Conditions were transitional from marine to estuarine (E. L. Yochelson, written commun., 1960) during deposition of the overlying Aarde Shale Member, which contains small foraminifers, Crurithyris, Hustedia, and other brachiopods, but none of the larger productids. The Church Limestone Member was deposited in fairly deep quiet water; however, the presence of algae and ostracodes indicates that the water became shallower near the end of Church time. Although conditions varied, the marine environment persisted until the end of Howard time: during deposition of the Winzeler Shale Member, many fenestrate bryozoans were preserved; during early Utopia time a very shallow water near-shore sublittoral environment is indicated by the presence of algal-coated myalinid pelecypods, but a more open sea (possibly with a firm bottom and swift currents) is suggested by the occurrence of Linoproductus, gastropods, and abundant ostracodes (E. L. Yochelson, written commun., 1960); and the fusulinid-bearing upper part of tlie Utopia Limestone Member probably represents a deposit in quieter water.

The sea retreated after Utopia time and left a thin accumulation of shallow-water near-shore marine sediments, which comprise the lowermost part of the White Cloud Shale Member of the Scranton Shale. Lithologic heterogeneity of the rocks, crossbedded sandstones, and channel deposits suggest that much of the Scranton, particularly the White Cloud, was probably deposited as a flood plain. Erosion in White Cloud time locally removed the entire Howard Limestone and an undetermined amount of the Severy Shale. Although minor readvances of the sea are recorded in the Happy Hollow and Rulo Limestone Members of the Scranton, conditions were dominantly nonmarine, and for a short period preceding deposition of the Rulo, part of the mapped area was a swamp in which coal formed. Algal-coated myalinid pelecypods and abundant ostracodes in the uppermost part of the Scranton indicate sublittoral to near-shore marine conditions which accompanied another widespread advance of the sea.

Deposits of the Wabaunsee Group above the Scranton Shale indicate a marked change in the rhythmic oscillations of the sea. The cyclic succession of lithologic units is less complex than in the Shawnee Group, and the limestone formations in the upper part of the Wabaunsee Group are composed of two limestone units separated by a claystone or siltstone unit.

The fauna indicates that most of the Burlingame Limestone Member of the Bern Limestone probably accumulated in water of normal salinity that at times was fairly quiet but at other times was vigorously circulated (E. L. Yochelson, written commun., 1960). The presence of algae and, locally, mollusks in the basal part suggests that the water was shallow in early Burlingame time.

The sea withdrew from this part of Kansas during deposition of the lower part of the Soldier Creek Shale Member of the Bern Limestone, and a swamp in which coal formed was present in part of the area. A marine fauna in the upper part of the Soldier Creek indicates a return of the sea--which remained in the area throughout Wakarusa time--but the complexity of the fauna indicates variations in depth of water, hardness of bottom, and velocity of currents.

Nonmarine rocks compose most of the Aulburn Shale in eastern Shawnee County and vicinity. The sea advanced into the area in late Auburn time and remained during deposition of the overlying Reading Limestone Member of the Emporia Limestone. A partial or perhaps total withdrawal of the sea occurred during at least part of Harveyville time; the presence of well-preserved plants and abundant smooth ostracodes in the member a short distance west of the mapped area suggests a fresh-water pool or swamp environment (E. L. Yochelson, written commun., 1960). Algae, ostracodes, and myalinid pelecypods indicate that the sea was extremely shallow at the beginning of Elmont time; however, the water was deeper during deposition of the upper fusulinid-bearing part of the Elmont Limestone Member of the Emporia.

All strata of the Willard Shale except those in the basal few feet seem to be of nonmarine origin; thus, a rapid retreat of the sea at the end of Elmont time is indicated. The apparent lack of marine sediments at the top of the Willard and the lack of a near-shore fauna in the basal part of the overlying Tarkio Limestone Member of the Zeandale Limestone suggest a rapid advance of the sea. Most of the Tarkio is fusulinid-bearing limestone that probably was deposited in quiet water. A marine fauna in thin limestone beds in the lower part of the overlying Wamego Shale Member of the Zeandale indicates that a shallow sea covered this area during most, if not all, of Wamego time. The bioclastic limestone of the overlying Maple Hill Limestone Member, with its many fusulinids, crinoid debris, brachiopods (but no productids), small fragments of bryozoans, and algae, suggests deposition in relatively shallow water in which current action was vigorous but not strong enough to give the fusulinids a preferred orientation (E. L. Yochelson, written commun., 1960).

A change to nonmarine conditions after Maple Hill time is postulated for deposition of most of the Pillsbury Shale; however, the sea returned near the end of Pillsbury time, and fusulinid-bearing claystones were deposited immediately below the Dover Limestone Member of the Stotler Limestone. The Dover contains abundant fusulinids, horn corals, and biscuit-shaped algal masses. The marine conditions continued to prevail at least through deposition of the lower part of the overlying Dry Shale Member of the Stotler--the youngest exposed rocks in the mapped area.

Eastern Shawnee County and vicinity lies in the western part of the Forest City basin--a structural basin east of the Nemaha uplift in the northeastern part of Kansas and neighboring parts of Missouri, Nebraska and Iowa--that formed mainly after Mississippian time (Lee, 1943, p. 13). The mapped area is east of the axis of the basin. Outcropping rocks strike approximately N. 20°-300° E, and dip northwest, generally 20-40 feet per mile. The northwestward dip is interrupted slightly by minor folds that generally trend northwestward. The structural relief is about 500 feet. A few small structures occur with less than 20 feet of closure. The structure pattern in the area is shown on the geologic map (pl. 1) by contours drawn at 20-foot intervals on the base of the Topeka Limestone.